The present disclosure relates to a drilling fluid particularly suitable for deep water (e.g., deep-sea) drilling operations having extreme temperature conditions at particularly difficult depths. In particular, water-based drilling fluids are usually not a viable option due to poor drilling performance, mainly caused by wellbore instability. Use of conventional non-aqueous drilling fluids such as diesel or synthetic-based fluid are problematic due to environmental concerns related to the disposal of contaminated drill cuttings, in particular toxicity and biodegradation of the oil-based drilling fluids.
On both offshore (deep water) and inland drilling barges and rigs, drill cuttings are conveyed up the drill hole by a drilling fluid. With non-aqueous drilling fluids, the cuttings are necessarily contaminated with an adherent film or layer of drilling fluid, which typically penetrates into the interior of the cuttings. This is true despite the use of various vibrating screens, mechanical separation devices and various chemical and washing techniques.
Currently, in outer continental shelf waters of the U.S., cuttings drilled using non-aqueous drilling fluids are prohibited from discharge unless they are in compliance with the EPA specified protocol for meeting technology-based standards associated with discharge of cuttings associated with synthetic based drilling fluids. Non-aqueous drilling fluids that do not meet these standards require an alternate method of disposal, most of which are far more expensive and more logistically difficult than local discharge of drilling cuttings. For example, if cuttings cannot be discharged offshore then they must be boxed and shipped to an onshore facility, which is very difficult and expensive in most regions.
The EPA requires that a drilling base fluid must exceed the performance of one of two identified synthetic fluid standards, a C1618 internal olefin (C1618 IO) and C8-C16 fatty acid/2-ethylhexyl esters, in the 275 day anaerobic biodegradation test (i.e. have higher biodegradation) and the 10 day sediment toxicity test using Leptocheirus plumulosus (i.e. have lower toxicity). At the present time, the only non-ester based SBF's that satisfy the requirements are C1618 IO and C1518 IO.
However, environmental and economic concerns have prompted the development of new drilling fluids. Blends of olefins and esters are being developed in response to the guidelines for a balance between technical requirements, cost, and environmental performance. However, supply issues have driven up the cost of C1618 internal olefin and esters are not particularly desirable because they are hydrolytically unstable and become unusable due to thickening under conditions found in deeper water operations. New synthetic-based drilling fluid blends are required to help ensure availability of EPA compliant drilling fluids, while satisfying technical requirements for fluids used in deep water operations.